Answer: It sounds like a type of rose canker. Many types of fungi cause canker on roses. Although widespread in our area, canker is rarely a serious disease. The fungus enters older rose stems through pruning cuts and wounds in the bark. Once the plant is infected, the bark turns yellow, wrinkles, splits and eventually dies. The purple ring around the stem is often a sign of the infection. If only a few branches are affected and the damage doesn't reach the bud union, prune out the diseased stems a few inches below the last sign of infection and destroy them. Disinfect your pruners with a 1% bleach solution between cuttings to avoid spreading the disease. If all the branches are infected or if the infection goes below the bud union, remove and destroy the rosebush and plant. Canker isn't very contagious, so it's not likely to infect any healthy roses growing nearby. There aren't any resistant rose varieties, but you can reduce the risk of your roses getting canker by avoiding physical damage to the stems, making clean pruning cuts and planting in a well drained, sunny location.
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